It is known to make a fuel tank with a shell of thermoplastic material that is blown, thermoformed, or rotormolded, for example.
Such a shell can include a layer that forms a barrier against hydrocarbons so as to limit hydrocarbon losses by diffusion through the shell.
Such a barrier-forming layer can be made of ethylene-vinyl alcohol copolymer (EVOH).
There exists a need to secure elements, such as a valve for venting air or degassing, for example, on the inside face of the shell of the tank, regardless of whether or not the shell includes a barrier-forming layer.
Where appropriate, this should be done without damaging the barrier-forming layer.
In addition, the reliability of such a connection must be guaranteed throughout the lifetime of the tank, in spite of the vibrations to which the tank is subjected and any dimensional variations to which the shell might be subjected in particular under the effect of the thermoplastic material swelling on contact with hydrocarbons.
The present invention seeks to provide a reliable connection.
The invention achieves this by a novel motor vehicle fuel tank comprising a shell, and inside the shell at least one add-on element such as a valve, wherein the shell presents a portion in relief, wherein the add-on element is connected to the shell by means of an intermediate element including at least one elastically-deformable portion arranged to engage, after being elastically-deformed, in or on said portion in relief so as to hold the intermediate element to the shell, and wherein the add-on element is arranged so as to be connected to the intermediate element in such a manner as to prevent the elastically-deformable portion of the intermediate element from being subjected to inverse elastic deformation enabling it to become disengaged from said portion in relief.
The elastically-deformable portion of the intermediate element is held in a predetermined position when the add-on element is secured to the intermediate element, and while held in this way it prevents any displacement of the intermediate element in a direction leading to disengagement of the portion in relief of the shell of the tank.
The invention thus makes it possible to provide a locking system that is effective on securing the intermediate element in or on the portion in relief of the shell of the tank, and consequently of ensuring that the add-on element is held in stable manner.
In a preferred embodiment, it defines a housing in which the elastically-deformable portion of the intermediate element is suitable for being engaged.
Still in a particular embodiment, the above-mentioned housing communicates with a lateral passage enabling a lateral extension of the intermediate element or of the add-on element to be received.
This makes it possible to establish a keying system to guarantee that the add-on element is in a predetermined orientation once it has been secured to the shell of the tank.
In addition, where appropriate, the tank can be made more compact by reducing the axial extent of the add-on element, since the above-mentioned passage makes it possible to bring the portion of the add-on element constituting the above-mentioned lateral extension into the vicinity of the shell of the tank.
This embodiment also makes it possible to secure the add-on element substantially at the highest point of the tank, which is particularly advantageous when the add-on element is an air vent or degassing valve.
In a particular embodiment, the lateral extension in question is constituted by an endpiece for connection to a pipe.
The passage receiving the endpiece is then advantageously defined by walls that are substantially parallel to the axis thereof.
Still in a particular embodiment, the opening of the housing through which the intermediate element is inserted is not circularly-symmetrical, thus making it possible to secure the intermediate element in a predetermined angular position once it is engaged in the housing. In a variant, said opening can be circularly-symmetrical.
In a particular embodiment, the intermediate element is arranged to snap-fasten in the housing in the axial direction thereof.
The intermediate element can thus have elastically-deformable fastening tabs suitable for snap-fastening in the above-mentioned housing.
The intermediate element can thus be secured to the shell of the tank in a manner that is simple and fast.
In a particular embodiment, the intermediate element has at least two resilient tabs leaving a gap between them and arranged so as to snap-fasten in the housing formed by the shell of the tank, the add-on element including a locking portion suitable for engaging in said gap in such a manner as to prevent the tabs from moving towards each other and disengaging from the housing.
This embodiment is advantageous because the shell of the tank is likely to be subjected to variations in its dimensions over its lifetime.
In the absence of the above-mentioned locking portion, there would be a risk of the tabs disengaging from the housing in which they have been inserted.
In a particular embodiment, the intermediate element has two pairs of resilient tabs, each pair being disposed facing the other, the tabs in a given pair being disposed in such a manner as to come into contact with the same face of the housing.
In a variant, the intermediate element extends along a longitudinal axis and has a plurality of resilient tabs disposed at equal angular intervals around said longitudinal axis.
Still in a particular embodiment, the housing has an axial section of dovetail shape and the tabs are of flattened shape being angled outwards so as to fit substantially to the shape of the inside faces of the housing.
This configuration makes it possible to have a large bearing area for the resilient tabs and the inside faces of the housing, thereby improving the reliability of the connection.
Advantageously, the add-on element is arranged to snap-fasten on the intermediate element.
In a particular embodiment, the intermediate element has a tubular body with an elastically-deformable portion at one end for engaging in the above-mentioned housing, and the add-on element is arranged to connect to the inside of said tubular body.
The intermediate element and the add-on element preferably include portions in relief arranged to co-operate so as to enable the add-on element to be preassembled in the intermediate element before the intermediate element is connected to the shell of the tank.
Advantageously, the tubular body of the intermediate element has recesses and the add-on element has teeth suitable for snap-fastening in the recesses.
Preferably, the intermediate element has a first set of recesses disposed in such a manner as to enable the add-on element to be held in a first position relative to the intermediate element suitable for enabling the intermediate element to be put into place on the shell of the tank, and a second set of recesses enabling the add-on element to be held in the intermediate element in a second position relative to the intermediate element, said second position of the add-on element preventing the intermediate element from becoming detached from the shell of the tank.
This enables the add-on element to be connected in simple and low cost manner inside the intermediate element.
In a particular embodiment, the add-on element has an endpiece and the tubular body of the intermediate element has a window for passing said endpiece.
Advantageously, the window is set back from the end of the tubular body situated remote from the elastically-deformable portion.
Thus, the intermediate element retains good mechanical strength because of the strip of material situated between the above-mentioned window and the end of the tubular body.
In a particular embodiment, the shell is made by blowing a thermoplastic material. Advantageously, the shell then has at least one layer that forms a barrier against hydrocarbons.
In a particular. embodiment, the portion in relief for connecting the intermediate element is obtained by means of a predetermined shape being given to the blow mold.
In a variant, the portion in relief is obtained by overmolding an insert.
This embodiment is advantageous since the insert can form reinforcement opposing possible changes in the dimensions of the shell.
Also in a variant, the portion in relief can be obtained by fitting a fastener on the surface of the shell, which fastener can be heat-sealed to said surface.
By way of example, the add-on element is constituted by a valve or a check valve.
The invention also provides a method of manufacturing a motor vehicle fuel tank, the method comprising the following steps:
a) making a shell by shaping a plastics material, in particular by blowing, thermoforming, rotomolding, or injection molding a thermoplastic material;
b) making a portion in relief on the shell, during or after formation of the shell;
c) connecting an intermediate element to said portion in relief, the intermediate element being provided with at least one elastically-deformable portion arranged to engage by resilient deformation in or on said portion in relief so as to hold the intermediate element to the shell; and
d) connecting an add-on element to the shell of the tank at the same time as the intermediate element or thereafter, said add-on element being suitable for preventing the elastically-deformable portion of the intermediate element from moving in such a manner as to enable it to become disengaged from said portion in relief.
After the intermediate element has been put into place on its own on the shell of the tank, the add-on element can be connected to the intermediate element to prevent the elastically-deformable portion of the intermediate element moving in such a way as to enable it to disengage from the portion in relief.
In a variant, the add-on element can be preassembled to the intermediate element before the intermediate element is put into place on the portion in relief, the intermediate element can then be connected to the portion in relief, and finally the add-on element can be moved relative to the intermediate element in such a manner that the add-on element prevents the elastically-deformable portion of the intermediate element from moving in such a way as to enable it to disengage from the portion in relief.